I have a 93 eg bubble with a b18 head & b20 block. The headers i bought fit too low & in time will get damage with st wear. For what engine should i get headers that wont be that low? & also i noticed it doesnt fit to my original exhaust cat, any advise on the full exhaust switch?

 

All b18 & b20 are similar in deck height. Difference, if any are 1-3mm. You won't notice. If your header is too long and doesn't have enough clearance with street it should be a header design.

Take the car to a shop and have the custom fit to the cat.